A high-frequency power inductance element such as a high-frequency power transformer and a choke coil is often used in, for example, an inverter-type power supply device which processes electric source by temporary conversion of the source to high frequency. This type of inductance element is required to have smaller interwinding capacity and satisfactory radiative heat dissipation for processing high power or large current with high frequency. Further, in order to assemble a compact and low cost power supply device and the like using an inductance element, there is preferred a configuration where the inductance element is capable of being mounted directly on a printed circuit board, particularly a configuration adapted for surface mounting.
As a conventional type of inductance element, as described in Japanese Patent Application Laid-open Publication No. 2000-223320 for example, there have been those having a structure where oblate-sheet shaped one-turn coils are formed from a copper sheet stamped out as substantially a U-shape (or a C-shape), and are laminated with insulating sheets, and where a pair of E-shaped cores (magnetic cores) are fit by insertion into the laminated one. Both end portions of the respective one-turn coils are integrally formed with terminal portions, and a coil with a predetermined number of turns (or a predetermined inductance value) is capable of being formed by appropriately connecting the terminal portions.
Further, an edgewise coil has also been used as the above coil. The edgewise coil is formed of a rectangular copper strip spirally wound a predetermined number of times, the wider surfaces of which are overlapped with a predetermined interwinding space. The entire winding of the edgewise coil is integrated continually, so that electrical resistance of the coil is capable of being made smaller than that of a coil formed of one-turn coils laminated and connected.
However, for a conventional high-frequency power inductance element in which a coil thereof is formed of oblate-sheet shaped one-turn coils laminated, there has been required a step of laminating a plurality of the one-turn coils with insulating sheets while positioning the one-turn coils mutually, and there has further been required a step of connecting the one-turn coils. Therefore, in the conventional high-frequency power inductance element, there has been a problem that assembling is troublesome and productivity is low. Further, since the insulating sheets laminated with the one-turn coils prevents radiative heat dissipation from the one-turn coils, there has also been a problem that radiative heat dissipation is low.
Further, for a conventional high-frequency power inductance element in which an edgewise coil is used, since a step of winding the coil while overlapping the wider surfaces of a rectangular copper strip of the coil is difficult, there has been a problem of low productivity of the coil. Further, in order to stably retain interwinding space of the edgewise coil, it is necessary to intervene sheet insulator between the strips. However, the intervention of the insulator causes a problem of obstructing radiative heat dissipation from the coil, which is similar to the problem in the above-described laminated type.
In both the above-described two types of inductance elements, since the interwinding space of the coil windings has a structure in which the wider surfaces of the rectangular copper strip face each other, there has been a problem that interwinding capacity of the inductance elements is large, and that as a consequence, leakage of electromagnetic noise of the inductance elements used as a high-frequency power transformer or a choke coil is large due to such interwinding capacity.